Stitched sheet product



R. S. OWENS STITCHED SHEET PRODUCT Filed June 30, 1944 s n E w Patented July 11, 19

7 2,514,412 s'rrrc sneer rnon'oc'r Robert S. Owens, Brooklyn, N. Y.

Application June 30, 1944, Serial No. 543,000 6 Claims. (01. 10298) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

The invention relates to the manufacture of assembled sheet products of thermoplastic or solvent materials and more specifically to the production of explosive products having the form of thin sheets of explosive stitched together for various reasons, using sewing machines similar to those employed for stitching together other materials of corresponding thickness. In particular, the invention is of high value in the production of what are known as increments," used as regular and/or supplemental propellant elements in the finned shells fired from Stokes mortars and similar weapons, as well as adapted to other projectiles and uses. At present the projectiles for such mortars are equipped with standard propellant cartridges having a primer exposed at the rear end of the fin assembly on the tail of the projectile and when the projectile is dropped tail first into the mortar, the firing pin in the head of the mortar detonates the primer and fires the propellant with a minimum or basic range. If increased range ls required, a greater amount of propellant is necessary, and this is supplied as one or more increments attached to the tail of the shell before it is dropped into the mortar. The conventional tail of the shell has fixed thereon a number of planiform radially disposed longitudinal fins having central apertures therethrough. The increment has consisted of a sort of book or pad consisting of from two to a multiplicity of flexible sheets of explosive laid in a pile and stitched together by a suitable thread. Usually in pads of small superficial area. a single row of stitches across the pile has been sufficient. The larger increment may have two rows of stitches suitably located.

While the superficial areas of the increment vary for different uses, for one use it comprises an area in the plane of the sheet approximately one and three-eighths inch square. The diagonals across this square measure substantially more than the distance between the apertures of two mutually adjacent fins of a shell. The material of the increment has a good measure of inherent elasticity, so that when bent on the line of one diagonal the corners at the extremities of the other diagonal may be presented in the apertures of two mutually adjacent fins, and when the increment is relieved of the bending pressure it will tend to recover its planiform shape and so thrust opposite corners into the apertures 01 the fins, thereby supporting and retaining the increment on the projectile.

In the manufacture of certain increments, nitrocellulose, nitroglycerine, together with the usual stabilizers (and if required other ingredients compounded with same to give the desired ballistic effect) are colloided and rolled into relatively thin sheets on heated rolls. Other nitrated materials may -be used as may be preferred or hereafter developed. By one method, two or more of the sheets are then sewed together, as provided for in the specifications. After sewing, the sheets are cut into strips, parallel with the stitching and then are perforated to improve the burning qualities of the explosive and cut into squares crosswise of the stitching. They may be otherwise treated and converted into the desired finished product, which has relatively close tolerances as regards weight, size, and positions of perforations, the position of the stitching with relation to the perforations and the sides of the increments and finally the compliance of the stitching itself with the specifications.

The propellant value of an increment is a function of the number of sheets in the bundle or pack formed, and it is therefore of the utmost importance that the stitching be of dependable strength and capable of retaining the increment assembled, under long sustained rough jostling, extreme climatic conditions over long periods of time, and subject to solvent, corrosive, or other effects of the explosive which are highly deteriorating to some materials.

It is also important that the stitching thread be of such nature as not to afiect the explosive detrimentally.

Increments of the nature indicated have now become highly important in military operations involving the national defense and many thousand pounds are produced each month.

Incident to the manufacture of this material, owing to the fact that success of military operations depends on exact performance of the explosive and due to the great reliance placed on the results of its use, exacting requirements are made of manufacturers, including the Federal Government's own plants. In consequence, much material fails to meet specifications and on inspection is rejected, usually for reasons other than unsatisfactory quality as an explosive. The explosive sheet material in such rejected product as well as a large amount involved in trimming, is capable of reworking but has heretofore required dethreading, because the yarns used are not readily dispersible in the powder when sheeted -3 out in the rolling operations. This dethreading consists in removing the stitching applied, by manually drawing out the threads forming the stitches. This has proven a very expensive operation, requiring much hand labor and other expense, involving a cost over twenty cents a pound, and in addition impairing the health of employees with attendant medical cost and idle pay. The removal of the thread is required because it left in the material when reworked the explosive would be weakened by formation of lines specially liable tocleavage and materially affect its burning characteristics. This prior thread material also has caused frequent flash fires" during working on the rolls, when such thread was not completely removed. Such prior material left in the increment also tends to increase the flash effect. 1

It is therefore an object of this invention to embody and coordinate with the layered material a thread the body of which will be dispersible in or blendable with the explosive-perhaps largely homogeneous with the explosive-to the end that when reworked without dethreading, the value of the productwill not fall below the margin of allowable variation from standard.

It is a further important aim to embody a thread with an inert material of the necessary high tensile strength but forming such a small fraction of the whole material of the thread thatwhen taken with the remaining products of combustion of the manufactured producttolerance of ash contentof the explosive will not be exceeded.

It is a highly important aim to evolve a thread which will be of adequate strength and bending capability, and which can be used in sewing machines without involving excessive heating of the needles, since this is a factor which must be considered in this invention.

A further intent of the invention is to minimize impairment of the security of the fastening between the sheets of the increments due to shearing or cutting of the material by tight stitching in assembly of the sheets. This is sought from two angles: first to prevent cutting of the thread into the sheets by reason of the nature of the thread, and to minimize tendency of the sewing machines to draw the thread too tight; and, second, to present a thread which will so bond with the explosive sheet material that if the thread does become somewhat embedded in the superficial sheets, its major part will become so united therewith that risk of separation of the penetrated sheets from the remainder is minimized or obviated. The latter aspect is important because the thread tensioning devices of sewing machines will sometimes vary their setting without this becoming known until after large quantities oi work have been executed,-

which heretofore would result in'discard of the product involved, while with my invention much of such loss would be avoided. This liability is especially manifest in the fact that the machines operate in a room separated from the operators by a fire wall and can only be observed at a distance through small port holes.

It is also sought to limit the liability of cutting of the sheets by the thread, by so constituting the thread structure that the bulk of the thread will tend to prevent penetration of the sheets of explosive, and also under exceptionally tight stitching the thread will include a moderately yieldable sheath and a high tensile strength fiber in the thread and so that the sheath will be 4 moderately penetrated by such tension element of major strength before objectionable shearing of the sheet occurs. This also reduces the angle of bends of the major tension fiber elements in the thread which bends may tend to be accentuatedunder tight stitching.

Accommodation of tight stitching is particularly important because high speed sewin chines necessarily require firm stitching to avoid irregularities, which otherwise produce some stitches too loose followed by higher than normal tension in other stitches when slack in taken up.

It is also an aim to present a novel method of procedure whereby a peculiar bonding of the stitching and explosive sheets will be obtained as well as greater strength and reliability of the product generally.

At the same time that the above and other objects are attained it is sought to avoid modifying the characteristics, properties and qualities heretofore desired and inherent in the increments, but to attain these in higher degree.

Additional objects, advantages and features of invention reside in the construction, arrangement and combination of. parts involved in the embodiment of the invention, as will appear or be understood from the following description and accompanying drawings, wherein:

Fig. 1 is an elevation of a fragment of thread embodying my invention, greatly magnified;

Fig. 2 is a longitudinal section of the thread;

Fig. 3 is a fragmentary plan of a number of sheets stitched together preparatory to trimming and cutting into increments;

Fig. 4 is a plan view of a single completed increment;

- Fig. 5 is a cross section of the increment along the line of stitches;

0 Fig. 6 is a cross section on the line 0-4 of Fig. 4; 1nFig. '7 is a similar cross section after calender- Fig. 8 is a fragmentary plan of a large increment;

Fig. 9 is a view similar to Fig. 3 showing a portion of a pile of sheets stitched for large area increments;

Fig. 10 is a detail section of the finished increment at the loops of a stitch within the increment.

Shown in Fig. 4 is an increment ll, comprising a multiplicity of thin sheets it approximately of the thickness of heavy paper held together by a line of stitches i! such as may be made with a sewing machine adjusted to produce a very long stitch with a thread ll corresponding in outside diameter approximately to number thirty sewing thread or larger. (It is an advantage of my invention in one form that there is no inhibition oi the use of large thread as in the prior art.)

The finished stitched increment may consist of from two to thirty or more sheets, and may measure from one inch to three inches on each side and up to one-quarter inch or more thick. The thickness of the sheets-varies from .025 to .18 inch or more. The stitches are approximately one quarter inch long and do not require any special form or means to prevent \mravelling.

The increment usually has one or more perforations ll therethrough as before indicated to increase the area exposed and facilitate propagation of its explosion. The method of procedure in making up of sheets for the increments is well known as before described herein and that procedure may be continued with or without modification dictated by expediency or advance in the art.

In the sewing of the assembly of large sheets, practice is governed by usual requirements and expedients, particularly as to the use of a needle of ample size to form perforations which will admit the thread l8 therethrough readily.

As a preliminary to the production of my invention, I prepare a thread by procedures as disclosed in my U. S. Patent No, 2,243,917, employing fiber of high tensile strength resistant to corrosion and itself of a chemically inert material, in the present instance a fiber glass having unusually high tensile strength. This particular material is distinguished by exceeding fineness from prior glass fibers, approximating .00022-inch in diameter. It is available commercially from the Owens-Corning Fiberglas Corporation of Toledo, Ohio, under the trade name Fiberglas. A strand or thread H of the glass suitably spun is impregnated and coated as disclosed in the patent mentioned with a shroud or body 22 of a plastic material specially compounded of material or materials of such nature that they may be readily united integrally with the material of the sheet 16 by partial solution by the solvent still present in the material of the sheets IE; or, without material solution or softening of the shroud, by adhesion of the shroud and material I6 due to the opening or exposure of fresh surfaces of the latter incident to the perforation of the sheets l6 by the sewing machine needle; or by thermoplasticization incident to the heating of the materials by friction of the thread and needle in passing through the piled sheets, or by application of heat and pressure after the sewing operations are completed. Thus the coating of the thread must be one which will not be permanently or completely cured before the sewing occurs.

The materials which may be encountered in the sheet materials to be stitched are widely various. Double-base powder, and other compositions corresponding to those in trench mortar propellant increments, are examples of the thermoplastic materials used in explosive sheets which may have to be sewed; and among other thermoplastic sheets materials are nitrocellulose, cellulose acetate, phofilm, Pliofilm, etc. Among materials available as the impregnation and/or coating of thread for sewing explosive sheets either alone or in combination by admixture or by successive application, are nitrocellulose (single base powder, which may be used as both impregnator and sheath, or, solely as an impregnating material in the fiber element of the thread, after which the thread may be coated with some material of greater tensile strength), vinyl resin, Bakelite, nylon, and others. Polyester polamides, polyvinyl esters, phenol formaldehyde, resols, resitols, and others, are additional coating materials which may be found available as coatings and/or impregnators. As impregnators used alone or as additions to some of the above mentioned materials to assure good adhesion between the coating and tension fiber thread and particularly the glass yarn, there are available caoutchouc, buna, and other synthetic rubbers, balsam, pern, gum elemi, resin, pitch, and other adhesives flexible when set or cured. Acrylic acid resins are specially valuable for this purpose. These are preferably used only to an amount sufficient to coat the individual fibers of the tension fibers of the whole thread, and such application would be followed by formation of a shroud or external coating of strong tough material having a substantial measure of tensile strength, such as materials in the group named available for impregnating and coating of thread.

It is possible to use as a tension fiber in the thread of my new increment explosive, filaments of vinyl resin, nylon, cellulose acetate, rayon, Bakelite, or others of known high tensile strength synthetic fiber materials, such tension fiber being given a coating or shroud of single base powder of suitable composition or a coating of the same material as the tension fiber or other materials if compatible with and adapted to unite with the increment material in any of the ways before described herein, and which will be dispersible in, or will be toleratedby, the colloid mass of the increment. The principal purpose of this shroud is to obtain a yarn of thick enough diameter to materially reduce the tendency of the small diameter tension fiber yarn to cut the increment as well as to reduce the abrasive effect of the yarn on sewing machines and otherwise.

I prefer to use glass fiber of the kind above mentioned, however, as the tension fiber or yarn core of my thread, because it is dispersible in double base powder and because of its very high tensile strength, and its capability of bending adequately for the formation of stitches, and use in sewing machines, especially when coated as herein indicated.

An example of a thread for embodying the invention would be a yarn consisting of a suflicient number of filaments to supply a substantial part of the requirement of the specification of tensile strength set by the purchasing agency for the whole thread, allowing for the tensile strength of the coating to be applied and a margin of safety for imperfections. This yarn, conforming to' usual production practices heretofore developed, is treated with an impregnating material (heated, or in a solvent, to give high fluidity) to assure thorough penetration of the yarn, using a suitable adhesive material, so as to just very thinly coat or prime the external surfaces of. the yarn. The procedure and apparatus for effecting this is set forth in my patent above referred to, as well as the further steps now to be referred to.

After such impregnation the impregnated yarn is passed through a treatment or machine by which a coating or shroud of nitrocellulose is formed thereon to such thickness as to form a thread body of adequate cross sectional dimension for operation in sewing machines and as a shroud, shield, and cushion for the tension fiber to function as before described herein. Nitrocellulose suitably plasticized would be an alternative material for the shroud.

Another example would consist. of a tension element consisting of a suitable number of nylon fiber yarn, or cellulose acetate or other suitable yarn and a shroud of nylon or nitrocellulose applied so as at the same time to penetrate between the fibers, or applied as a shroud subsequent to a preliminary treatment with a more fluid nitrocellulose or with one of the special adhesive impregnators before mentioned.

In the case of the thread having the glass fiber tension element, the principal bulk constituent may be the shroud and yarn impregnation. The degree of nitration of the nitrocellulose shroud may be proportioned to a desired burning rate. The impregnation or cementing materials applied to the yarn core, if distinct from the double base powder, may be of such a nature as to tend to be absorbed by the latter, and also a similar interaction "and uniting may occur when a shroud of other materials is used in which there are solvents present when applied. Nitrocellulose, cellulose acetate, ethyl J cellulose, methyl cellulose, and like substances are available as shroud materials. 7

When caoutchouc is used as an impregnatoradhesive-cement, it may be applied either as a dispersion in water, as for example, latex or redispersed reclaimed rubber, or may be employed in a solvent mixture. The same is true of many synthetic so-called rubbers, and other like quality-substances. In either case the necessary compounding ingredients may be incorporated in, the coating and/ or impregnating solution or emulsion so that the compound will be either an air curing or a heat vulcanizable type, whichever is desirable. Uncured caoutchouc, when added to nitrocellulose, acts as a plasticizer and is readily dispersed in the increment when and if re-working of the latter and/or some other plastics, as indicatedherein, is required. Its quantity is so small that when the reworked material is again made up and stitched into increments the ballistic values will still meet the strict limitations and tolerances heretofore set up under contracts for production thereof.

In the use of glass fiber, the amount required is so minute that its presence in the finished increment will hardly be manifest by usual laboratory methods used to determine the presence of foreign material.

In those cases (including explosives) where the presence. of the fiber glass tends to exceed the folerance for foreign material, the tension fiber or yarn for incorporation in the complete thread may be of some of the organic materials such as indicated, as, polyester polamides, polyvinyl esters, phenolformaldehyde resols, resitols, resites or Novolaks.

In the assembly of increments in accordance with my invention, the same procedure is employed as heretofore followed in the prior art and before described herein. The stitching, cutting and punching produces increments of the same general appearance, size and mechanical quality as those heretofore produced, although it is possible to have the stitching less conspicuous or exposed, and the product will occupy less space in packing and shipment, especially if finally heatrolled.

There are also important distinctions or differences resultant, which are not superficially apparent. Thus, incident to the rapid operation of the sewing machine, the needle becomes warmed, and in the passage of the needle through the piled sheets the edges of the perforations become heated by the friction of the needle and thread thereagainst, and the thread shroud becomes similarly warmed, so that as soon as the stitches are formed and drawn taut, the warmth and pressure result in the thread sheath or shroud becoming joined with the sheet material as a unitary part thereof. Also, contrary to the effects manifest in the use of ordinary thread formed solely from silk yarn or cotton yarn, the shroud and the tension fiber at its core, so that the latter may partly compress the shroud portion under the fiber yarn against the confined sheet material, so that the non-extensible fiber does not come early if at all into contact with the sheet material and normally not at all; The shroud receives the initial shock when the thread draws taut in the work, causing the thread tensioning devices of. the sewing machine to yield and feed the thread without this shock or'shearing tendency reaching the severe degree present with ordinary thread, as will be appreciated from the fact that the compression and partial softening of the shroud occurs in the work, and that the tension yarn element may compress or partly cut into the shroud material.

. Further, by rolling the stitched product between heated rolls, either before or after cutting. or trimming, the shroud material is pressed flat into the body of the sheet material and into the needle perforations so that a more complete union of the thread material with the sheet is effected, and the rough prominence of thread heretofore manifest in the increments i eliminated making it possible to stack or pack the stitched material within a materially less space than before required, as well as making the increments so formed more'readily manipulated and minimizing liability of accident by the thread hooking on objects during handling.

While the appearance of powder increments is not a material factor in use of the explosive, such appearance may be material in the production of commercial articles of various kinds where plastic sheets are secured together for any reason, or where other materials are secured together with ties of a kind corresponding to the thread here disclosed.

By stitching the sheet material before it has become completely cured or while at a suitable temperature and with the thread in similar condition, the uniting of the two is enhanced without rolling or other heat application.

It should be understood that the intent of my invention as to the production of an explosive increment is to enable the production thereofusing a thread for stitching or tying therein, which, in addition to having the necessary tensile strength and size, will have as one of it basic components or as one at least of its principal ingredients a substance which-incident to reworking-is compatible with, or will blend with, or will be'tolerated by, the explosive of the increment or its colloidal components; or which on the heated rolls may be dispersed in the colloidal explosive material without noticeable detriment to the stability, appearance, or ballistic qualities of the product. In other words, the ideal thread for sewing the sheets together would be one of the same composition as, 'or contributing to the ballistic value of the increment. As a thread of the same composition a the known increment explosive might not have the required tensile strength to permit its use with sewing machines of present available manufacture, I have shown how other material having the necessary strength may be used as a tension member in the thread, yet preserving the advantage of ballistic values as indicated.

As indicated by the preceding and certain of the claims, the working referred to is one similar to that heretofore practiced in the rolling of bulk plastic stock or rejected or scrap stitched explosive sheet material (after hand extraction of the silk or other fiber thread heretofore used) to blend the material and give a finished sheet. This working consisted of passing the bulk rejected or scrap material back and forth between heated rolls in such manner that the material was kneaded and worked and united into a homogeneous stock batch similar to the original bulk new material from which the stitched sheets had been prepared.

The same treatment is accorded with my invention, but the rejects and scrap are reworked without any attempt to remove the stitching thread.

While it has been shown in the prior description that the glass fibers in my thread are capable of bending adequately to permit the form of stitching shown and described, it will be appreciated that the glass fibers are relatively brittle as compared to th flexibility and ductility of the plastic materials involved, especially when maintained at the temperatures ordinarily developed in reworking treatments.

When rejects and scrap stitched according to my invention are passed between the rolls, the relatively rapid surface movement of the plastic mass next against the rolls as compared to the movement of the material further from the rolls effects a continuing strain and deformation of the mass which results in a bending, twisting and rending of the glass fiber while the plastic mass is simply worked into a homogeneous unruptured mixture. Consequently after a moderate working, the particles of glass fiber thus become so reduced in size that they can not be distinguished in the sheets subsequently produced by final rolling similar to those originally used in the making of the rejected increments or from which the reworked scrap was trimmed. When differential rolls are used, the carrying through of part of the material abutting one roll at a speed much greater than that at which the material against the opposed roll moves, causes a more pronounced strain of the plastic, which the glass product can even less accommodate itself to, and so it is progressively severed or fractured by bendings, torsions, and stretching, until it becomes subdivided to an infinite degree.

The references to certain materials and their proportions in this description are exemplary, and it is not contemplated to limit the scope of the invention to any material or any group or class of materials except as may be specifically claimed. Insofar as the non-extensible material is concerned, it is intended to include within the scope of the claims herein all materials which have sufliciently high tensile strength, so that when they are used in sewing or otherwise in combining two or more sheets of materials together, if salvage of the combined or sewed materials is desired and may be performed by reworking, the thread member may be absorbed or dispersed so as not to have a deleterious effect on the aggregate of the reworked finished product.

In the larger increments, a slit 28 is cut radially from a large central opening 29 through one edge of the pad, so that the opposed portion may be twisted open to allow the increment to be engaged around the base of a shell to be retained thereon by closing of the opened part.

While the term yarn" has been used largely in referring to the high tensile strength element of my thread, it will be understood that the high tensile strength element may be a yarn in the cal sense. or a thread of more pronounced l twist made up of plies also twisted, so that a relatively hard twist may be employed.

I claim:

1. A stitched layered article comprising a plurality of plastic sheets secured together, the securing means comprising a stitching consisting of a high tensile strength adhesive-carrying yarn and a shroud thereon compatible with and blend= able with the material of the sheets.

2. An increment consisting of a plurality of sheets of plastic explosive superposed and secured, the securing means consisting of a thread of high tensile strength inert fiber in a quantity less than the allowable ash content of the increment, and a surrounding shroud of a combustible material, said thread being engaged back and forth through able with the material of the sheets.

3. An increment consisting of a plurality of sheets of plastic explosive superposed and secured, the securing means consisting of a thread of high tensile strength inert fiber in a quantity less than the allowable ash content of the increment and a surrounding shroud of a combustible material said thread being engaged back and forth through the pile of sheets and said shroud united integrally, with the abutting increment sheet material.

4. The combination of a plurality of sheets of flexible plastic in superposed relations and a stitching therethrough holding the sheets together and consisting of a thread comprising a tension element of major strength and minor bulk, and a binder of major bulk homogeneous with the said sheets.

5. The combination of a plurality of sheets of explosive in superposed relations and a stitching therethrough holding the sheets together and consisting of a thread comprising a tension element of major strength and minor bulk, and a binder of major bulk homogeneous with the explosive and having explosive characteristics.

6. A stitched sheet product consisting of a plurality of sheets of plastic material superposed and secured, the securing means consisting of a thread comprising a shroud blendable with the material of the sheets, and a high tensile strength yarn of fiber relatively brittle as compared to the material of the said sheets.

ROBERT S. OWENS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 864,725 Davis Aug. 27, 1907 1,274,258 Gerdom July 30, 1918 1,326,630 Barker Dec. 30, 1919 1,355,177 Sollen Oct. 12, 1920 1,989,495 Peake Jan. 29, 1935 2,063,572 Woodbury Dec. 8, 1936 2,210,959 Storm Aug. 13, 1940 2,243,917 Owens June 3, 1941 2,313,058 Francis Mar. 9, 1943 2,341,019 Cook Feb. 8, 1944 2,353,960 King July 18, 1946 FOREIGN PATENTS Number Country Date 9,481 Great Britain of 1899 6,103 Great Britain of 1902 

